Continuously variable stepped transmission

ABSTRACT

A continuously variable transmission for use with motor vehicles includes and electronic control unit, and automated gear unit, a variator, an input gear set, an input fixed ratio element and an output fixed ratio element. The electronic control unit is configured to include logic rules for controlling a transmission, the logic rules including issuing transmission control commands. The automated gear unit has gears providing a plurality of selectively engaged gear ratios and engages one of the plurality of gear ratios responsive to commands from the electronic control unit to do so. The gear unit has a gear unit input shaft and a gear unit output shaft. The variator has a variator input shaft and a variator output shaft. The variator is configured to continuously vary a ratio of input torque to output torque between the variator shafts responsive to commands from the electronic control unit. The variator output shaft is drivingly connected to the gear unit input shaft. The input gear set is drivingly connected to the variator input shaft. The input fixed ratio element is configured to reduce the torque from the input gear set to the variator and is operably disposed between the input gear set and the variator input shaft. The output fixed ratio element is configured to increase the torque from the variator and is operably disposed between the variator output shaft and the gear unit input shaft.

RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/423,085, filed Nov. 1, 2002 entitled “ContinuouslyVariable Stepped Transmission”, which is incorporated herein byreference in its entirety.

FIELD OF THE INVENTION

[0002] The present invention relates to multi-speed transmissions usedin combination with continuously variable transmissions or CVTs. Inparticular, the present invention relates to the use of a CVT between anengine and a multi-speed transmission.

BACKGROUND OF THE INVENTION

[0003] Trucks, particularly heavy duty trucks, commonly employ multiplespeed counter-shaft type mechanical transmissions having up to at least18 different torque multiplication ratios. The large number of ratios isneeded to enable a fully loaded truck to perform a variety of necessarytasks, including low speed maneuvering in forward and reverse gears asrequired for moving about freight yards and for loading and unloadingtasks, accelerating from a dead stop, accelerating while rolling,maintaining speed while on a grade, and so on. The large number of gearsmeans that there is a frequent need for shifting. Manual gear shifting,as well as the selection of the correct gear, are tasks which requireconsiderable operator experience to consistently execute optimally.Increasingly, transmissions for heavy-duty trucks are being automated.However, even with a large number of ratios, and automated shifting, theengine speed varies with the speed of the vehicle when the vehicle is ina given gear ratio. This means that the engine's operating parametersmust be compromised to accommodate the anticipated range of engineoperating speeds. An engine that could be tuned to operate at a singleengine speed could be tuned to operate much more efficiently. Shiftingdecreases the operating efficiency of the vehicle, as there can istypically a dip in vehicle speed during the shift when the engine ismomentarily disconnected from the drive wheels, and a subsequent need tobring the vehicle back to its target speed.

[0004] It is desired to provide a transmission which provides a fullratio coverage, yet minimizes the need for shifting. It is alsodesirable to provide the engine with a narrower anticipated speedoperating range so as to permit the optimization of engine parameters.One of the limitations to the use of CVTs has been their limited torquecapacity. One approach to dealing with the relatively low torquecapacity of CVTs is to reduce the torque sustained by the CVTs. This hasbeen achieved by splitting the drive torque from the engine into twocomponents, with only part of the torque going through the CVT. Aplanetary system is commonly used to recombine the CVT and directtorques. The result of such a power splitting arrangement is that, whileit provides a relatively high torque capacity CVT system, that systemhas a relatively narrow torque multiplication ratio band. The narrowratio concern has been overcome by combining the CVT power splittingsystem with a multi-step ratio transmission. One such system isillustrated in U.S. Pat. No. 5,167,591, the teachings of which arehereby included by reference. It illustrates the use of a torquesplitting planetary arrangement in combination with a steppedtransmission. However, given the high torque outputs of engines used forheavy duty trucks, and the limited torque capacities of know CVTsystems, particularly CVT belt-type systems, further torque reductionwas necessary. It is also desired to provide a compact packagingarrangement for such a system.

SUMMARY OF THE INVENTION

[0005] The inventive system beneficially reduces the need for shiftingby using the CVT to expand the operating range of each of the steppedgears in the automated gear unit. This is achieved in spite of thelimited torque capacity of the CVT by subjecting the CVT to only aportion of the high torque levels of the engine. A step-down gear setreduces the torque passing through the CVT, and then passing the torquefrom the CVT through a step-up gear set which restores the torque. TheCVT is further protected by splitting the torque from the engine, andrecombining in a planetary gear set. The planetary gear set serves tomix or combine the direct torque element from the engine with the torquefrom the CVT.

[0006] A continuously variable transmission for use with motor vehiclesincludes and electronic control unit, and automated gear unit, avariator, an input gear set, an input fixed ratio element and an outputfixed ratio element. The electronic control unit is configured toinclude logic rules for controlling a transmission, the logic rulesincluding issuing transmission control commands. The automated gear unithas gears providing a plurality of selectively engaged gear ratios andengages one of the plurality of gear ratios responsive to commands fromthe electronic control unit to do so. The gear unit has a gear unitinput shaft and a gear unit output shaft. The variator has a variatorinput shaft and a variator output shaft. The variator is configured tocontinuously vary a ratio of input torque to output torque between thevariator shafts responsive to commands from the electronic control unit.The variator output shaft is drivingly connected to the gear unit inputshaft. The input gear set is drivingly connected to the variator inputshaft. The input fixed ratio element is configured to reduce the torquefrom the input gear set to the variator and is operably disposed betweenthe input gear set and the variator input shaft. The output fixed ratioelement is configured to increase the torque from the variator and isoperably disposed between the variator output shaft and the gear unitinput shaft.

[0007] A continuously variable transmission for use with motor vehiclesincludes and electronic control unit, and automated gear unit, avariator, and a planetary mixer gear set. The electronic control unit isconfigured to include logic rules for controlling a transmission, thelogic rules including issuing transmission control commands. Theautomated gear unit has gears providing a plurality of selectivelyengaged gear ratios and engages one of the plurality of gear ratiosresponsive to commands from the electronic control unit to do so. Thegear unit has a gear unit input shaft and a gear unit output shaft. Thevariator has a variator input shaft and a variator output shaft and isconfigured to continuously vary a ratio of input torque to output torquebetween the variator shafts responsive to commands from the electroniccontrol unit. The planetary mixer gear set includes a ring gear and asun gear and a carrier. The carrier retains a plurality of planet gearswith the planet gears disposed between the ring gear and the sun gear.The ring gear is fixed to a mixer input shaft. The sun gear is drivinglyconnected to the variator output shaft. The carrier is fixed to a mixeroutput shaft which is drivingly connected to the automated gear unitinput shaft.

DESCRIPTION OF THE FIGURES

[0008]FIG. 1 is a schematic diagram of a drivetrain system including anengine, a CVT and a stepped transmission.

[0009]FIG. 2 is a plurality of superimposed plots of various operatingparameters of the inventive drivetrain system illustrating a first setof transmission characteristics.

[0010]FIG. 3 is a plurality of superimposed plots of various operatingparameters of the inventive drivetrain system illustrating a second setof transmission characteristics.

[0011]FIG. 4 is a combined perspective and sectional view of a CVTmodule joined to a gear unit.

[0012]FIG. 5 is an enlarged view of one portion of the CVT module andgear unit of FIG. 4.

[0013]FIG. 6 is a section view of the CVT module of FIG. 4 taken througha first axis and a second axis.

[0014]FIG. 7 is a sectional view of the CVT module of FIG. 4 takenthrough a first axis and a third axis.

[0015]FIG. 8 is a perspective view of the CVT module of FIG. 7.

[0016]FIG. 9 is a perspective view of the CVT module of FIG. 8 with aclutch housing.

[0017]FIG. 10 is a perspective view of the CVT module of FIG. 9 with avariator housing.

[0018]FIG. 11 is an exterior view of a combined CVT module and gear unitassembly.

DETAILED DESCRIPTION

[0019] Referring to FIG. 1, a vehicle drivetrain 10 including acontinuously variable transmission 12 and an electronically controlledinternal combustion engine 14 is illustrated. Continuously variabletransmission 12 is connected with engine 14 by a normally engaged masterfriction master clutch 16. Transmission 12 includes a CVT module 18 andan automated counter-shaft type mechanical transmission gear unit 20.

[0020] An exemplary gear unit 20 is of the type sold by EatonCorporation, the assignee of this invention, under the name AutoShift®.A seven speed model (Model numbers TO-11607-ASX and TO-14607-ASX) isused as one exemplary embodiment of gear unit 20. Units or transmissionssuch as exemplary unit 20 are well known in the prior art and may beappreciated by reference to U.S. Pat. Nos. 3,105,395, 3,283,613 and4,754,665, the disclosures of which are incorporated by reference. Itshould be appreciated that any transmission featuring a plurality offixed gear ratios and automatic shifting and having the necessary torquecapacity is suited for use in place of the described exemplary gear unit20. For example, the plots of FIG. 2 are based on a conceptual fivespeed transmission. Conceivably, units employing more or fewer gearratios could be employed, depending on the torque and speed requirementsof the vehicle. However, regardless of the configuration of the gearunit selected, the gear unit selected must have fixed gear ratioscompatible with the ratio range of the CVT module 18 as will bedescribed in more detail below.

[0021] Transmission 12 and engine 14 each have an electronic controlunit (ECU) 22 and 24 respectively. ECUs 22 and 24 communicate with eachother and a system ECU 26 over multiplexed data buses 28 and 30. Bus 28is disposed between system ECU 26 and transmission ECU 22. Bus 30 isdisposed between system ECU 26 and engine ECU 24. ECUs 22, 24 and 26 maybe of the type illustrated in U.S. Pat. No. 4,595,986, the disclosure ofwhich is incorporated herein by reference. The ECUs are effective toprocess the inputs from a variety of sensors discussed in more detailbelow in accordance with predetermined logic rules, to issue commandoutput signals to the other ECUs and to a transmission shift controller32 and an engine controller 34 and/or to a display unit and/or to othersystems. Engine controller 34 controls, among other parameters, enginefueling. The data buses 28, 30 conform to an appropriate industrystandard communications protocol for data links such as SAE J-1922, SAEJ-1939, ISO 11898, ISO 11783 or the like.

[0022] Information indicative of engine torque, engine speed andtransmission output shaft speed will be carried to the ECUs 22 and 24 byconductors 36 disposed between a plurality of sensors and the ECUs. Thesensors include an engine crankshaft speed sensor 38, a CVT module inputshaft speed sensor 40, a CVT module output shaft speed and gear unitinput shaft speed sensor 42, a gear unit output shaft sensor 44, aposition sensor 46 for a fuel pedal 47, a master friction clutchposition sensor and various engine and transmission parameter sensors.Conductors 36 also communicate command signals to the various systemcontrols and actuators including gear unit shift controller 32, enginecontroller 34 and a master friction clutch actuator 48. The masterfriction clutch sensor is, in the exemplary embodiment, integrated intoactuator 48, but may be separate from actuator 48. As controllers 32 and34 and actuator 48 typically comprise portions of closed loop systems,provisions may be made for conductors 36 to handle both for controlsignals and feedback signals. Alternatively, separate conductors, notshown, may be provided. Further, controllers 32 and 34 may also includeintegral position sensors as may be needed.

[0023] Clutch actuator 48 controls master clutch 16 responsive tocontrol signals from transmission ECU 22. Such systems are well known.See U.S. Pat. Nos. 4,081,065 and 4,361,060, the disclosures of which areincorporated herein by reference. Alternatively, master clutch 16 may bea centrifugal clutch of the type disclosed in U.S. Pat. No. 6,502,476not requiring an actuator, the disclosures of which are incorporatedherein by reference. Master clutch 16 need not be disengaged for eachshift. Fuel modulation, as disclosed in U.S. Pat. No. 4,850,236, may beutilized for shifting gear unit 20 without releasing the master clutch.

[0024] A shift selector 49 allows the vehicle driver to select a mode ofoperation and provides a signal indicative of the selected mode.Possible modes include Park, Reverse, Neutral, and Drive. Shift selector49 includes a plurality of gear range buttons, which may be selected bythe vehicle operator. Shift selector 49 could take other forms notshown, such as a conventional automatic transmission shift lever whichmoves in a fore-aft direction between positions corresponding to gearranges.

[0025] An input shaft brake 50 is mounted to transmission gear unit 20and facilitates quicker upshifting as is well known in the prior art.Input shaft brake 50 is responsive to control signals from transmissionECU 22.

[0026] CVT module 18 has as its principal elements a variator 52 and aplanetary mixer or gear set 54. Engine crankshaft 56 of engine 14 isselectively drivingly connected by master friction clutch 16 to a CVTmodule input shaft 58 or mixer input shaft 58. Input shaft 58 rotatesabout a first axis of rotation 59 on which it is centered. A ring gear60 is fixed to input shaft 58. A variator input gear set 62 drivinglyconnects input shaft 58 with variator 52. Input gear set 62 includes aninput drive gear 64 fixed to input shaft 58 and an input driven gear 66fixed to a variator input shaft 68. Input shaft 68 is rotatably fixed toa first variator pulley 70 for unitary rotation therewith. Gear 66,shaft 68 and pulley 70 are centered on and rotate about a second axis ofrotation 69 which is parallel to but offset from first axis 59.

[0027] First variator pulley 70 is drivingly connected to a secondvariator pulley 72 by a drive belt or chain 74. Drive chain 74 in apreferred embodiment is of the type employed in the Multitronic™continuously variable transmission in the Audi A6® car. The Multitronic™transmission employs pulleys, chain, and hydraulic pulley controlssupplied by LuK Lamellen und Kupplungbau GmbH of Germany (LuK) and itssubsidiaries and affiliates. Such elements are taught and described inU.S. Pat. Nos. 5,169,365; 5,201,687; 5,217,412; 5,295,915; 5,538,481;5,667,448; 5,725,447; 6,017,286; 6,068,565; 6,123,634; 6,129,188;6,171,207; 6,174,253; 6,186,917; 6,190,274; 6,234,925; 6,270,436;6,293,887; 6,322,466; 6,336,878; 6,336,880; 6,346,058; 6,358,167;6,358,181; 6,361,456; 6,361,470 and 6,416,433, all of which are owned byLuK or its affiliates or subsidiaries, the disclosures of which areincluded herein by reference. Pulleys 70 and 72 each have facing conicalflanges which can be selectively axially moved toward and away from eachother. The radius of engagement between the chain and the pulleys isdetermined by the distance between the flanges. The closer the flangesare to each other, the larger the effective pulley diameter is. Becausethe length of chain 74 and the center-to-center distance of pulleys 70and 72 are fixed, changes in the effective pulley diameter of one pulleymust be co-ordinated with changes in the effective pulley diameter ofthe other pulley. While pulleys 70 and 72 are shown as being of equalsize, they need not be, particularly if it is seen as advantageous tooperate principally in either the overdrive mode or the underdrive mode.The displacement of the flanges is ultimately controlled by commandsignals from the transmission ECU 22. It is to be appreciated that thetype of variator 52 employed is exemplary only. Alternative types ofvariators which may be employed include other types of variable diameterbelt and pulley variators, pump/motor variators, toroidal typevariators, and all other mechanisms capable of suitably varying torqueand speed on a continuous basis.

[0028] The overall ratio range provided by one embodiment of pulleys 70and 72 is approximately 6:1. In doing so, pulley 70 and 72 provide bothan underdrive condition with a torque multiplication factor of about2.45:1, and an overdrive condition with a torque multiplication of about1:2.45. In the direct condition, with both pulleys 70 and 72 having thesame effective pulley diameter, the torque multiplication factor is 1:1.The underdrive condition is achieved with pulley 70 in a minimumdiameter condition in which the flanges of pulley 70 are spreadrelatively far apart and pulley 72 in a maximum diameter condition inwhich the flanges of pulley 72 are pushed relatively close together. Theoverdrive condition is achieved with pulley 70 in a maximum diametercondition in which the flanges of pulley 70 are pushed relatively closedtogether and pulley 72 in a minimum diameter condition in which theflanges of pulley 72 are spread relatively far apart.

[0029] A hydraulic controller 76 is employed to translate the electroniccontrol signals from ECU 22 transmitted via conductors 36 intopressurized hydraulic fluid passing through hydraulic connectingchannels 78. Pressurized hydraulic fluid from hydraulic controller 76mechanically displaces the flanges. It should be appreciated thatalternative means of displacing the flanges, such as electric motors,may be employed.

[0030] A variator output shaft 80 connects second variator pulley 72with a variator output gear set 82. Output gear set 82 includes anoutput drive gear 84 and an output driven gear 86. Shaft 80, pulley 72and drive gear 84 all rotate about a third axis of rotation 87 which isparallel to but offset from both first and second axes of rotation 59and 69. The functions provided by gear sets 62 and 82 may alternativelybe provided by any other fixed ratio mechanism, such as sprocket andchain combinations, belts and pulleys or any other suitable mechanism.Output driven gear 86 is drivingly connected to a sun gear 88 ofplanetary mixer 54 by a connecting hub 90. At least two planet gears 92are disposed between sun gear 88 and ring gear 60. A carrier 94 on whichplanet gears 92 are rotatably mounted connect planet gears 92.

[0031] A CVT module output shaft 96 or mixer output shaft 96 isrotatably fixed to or is unitary with a gear unit input shaft 98 forrotation about axis 59. Hub 90 and gears 86 and 88 circumscribe shaft96, and also rotate about axis 59. A gear unit output shaft 100 extendsfrom gear unit 20 for connection to a drive axle (not shown) or anintermediate drive shaft (not shown). The relative rate of rotationbetween input shaft 98 and output shaft 100 is determined by the gearselected within gear unit 20. Planetary gear set 54 beneficiallyprovides a greater diminution of torque transferred through variator 52by having ring gear 60 driven by input shaft 58 and having sun gear 86driven by variator 52 and having carrier 94 drive output shaft 96.

[0032] The continuously variable transmission 12 operates in thefollowing manner. The driver first selects a desired mode of operationusing the shift selector 49. The Drive mode is selected to provideforward motion. The selection is preferably made with the vehicle in astopped condition. The vehicle is equipped with a brake pedal (notshown) as well as fuel pedal 47. The brake pedal, when depressed,actuates the vehicle brakes which help maintain the vehicle in a stoppedcondition, and also bring the vehicle, when it is moving, to a stop. Inthe stopped condition, the vehicle operator may have his foot resting onthe brake. To accelerate the vehicle, the vehicle operator moves hisright foot to the fuel pedal 47 and depresses it. Controller 22 commandsthe engagement of master friction clutch 16. Torque from engine 14 istransferred through clutch 16 to input shaft 58. The torque is thensplit into two components, with a first part being transferred to ringgear 60 and a second part to variator 52 via gear set 62. The sum of thetorque transmitted by drive gear 64 and ring gear 60 equals the torquetransmitted by clutch 16. The torque from gear 64 is further reduced bythe ratio of gear set 62 before reaching variator 52. Reducing thetorque to the variator 52 by first splitting it with the planetary gearset 54, and further stepping down torque with gear set 62, and thenstepping up the torque from the variator with second gear set 82,beneficially allows the use of a relatively low torque capacity variatorto enable operation of a vehicle across a wide range of road speeds at aconstant engine speed. The variator, in an underdrive condition,multiplies the torque. Torque from the variator 52 is again increased bythe ratio of gear set 82, and transferred to sun gear 88. The combinedtorque of sun gear 88 and ring gear 60 is transferred to carrier 94through planet gears 92. It is the torque of carrier 94 which iscommunicated to input shaft 98. Gear unit 20 multiples the torque by theratio of the selected gear to generate the final output torque at outputshaft 100.

[0033] To start the vehicle moving, variator 52 has the flanges of thefirst variator pulley 70 spread relatively far apart and the flanges ofthe second variator pulley 72 pushed relatively close together toprovide a maximum variator torque multiplication. Gear unit 20 is infirst gear, providing the maximum gear unit torque multiplication of theengine torque transmitted by clutch 16. Together, variator 52 and gearunit 20 provide the necessary torque multiplication between engine 14and shaft 100 to initiate vehicle movement.

[0034]FIG. 2 shows the relationship between the rotational speed ofengine 14 and the rotational speed of various rotating components acrossa range of vehicle speeds. As used here, the word speed, when used inthe context of rotating shafts or elements, refers to the rotationalspeed of the shaft or element. Engine speed means the rotational speedof engine crankshaft 56. It is to be appreciated that a speed 102 ofinput shaft 58 equals the engine speed so long as clutch 16 is engaged.

[0035] Initially, with gear unit 20 in first gear, first gear providingthe greatest amount of torque multiplication of the available forwardgears, and with variator 52 providing the maximum amount of torquemultiplication within its capability, the speed 102 of input shaft speed58, the speed 104 of variator input shaft 68, the speed 106 of variatoroutput shaft 80, and the speed 108 of CVT module output shaft 96 allincrease linearly with vehicle speed 110 as the vehicle accelerates.However, that changes when input shaft speed 102 reaches an optimalengine speed 112. At optimal engine speed 112, input shaft speed 102plateaus or holds steady. When input shaft speed 102 plateaus, anacceleration of the CVT module output shaft 96, and hence of thevehicle, is maintained by varying the ratio of the variator 52.

[0036] Variator input shaft speed 104, which equals input shaft speed102 multiplied by the ratio of gear set 62, plateaus when input shaftspeed 102 plateaus. In the embodiment of FIG. 2, the ratio of gear set62 is approximately 1.6, with the speed of shaft 68 being 60% greaterthan that of shaft 58, and the torque transferred from shaft 58 to shaft68 being conversely reduced.

[0037] Transmission ECU 22 initiates adjust of the diameters of pulleys70 and 72 at the initiation of the plateau so as to maintainacceleration. Pulley 70, rotating at variator input shaft speed 104,increases in diameter as pulley 72 decreases in diameter, increasing thespeed of pulley 72. The speed of pulley 72 is decreased, while thetorque is correspondingly increased, by transmitting it through variatoroutput gear set 82. In the example of FIG. 2, the ratio of gear set 82is approximately 0.50:1, with the speed of hub 90 and sun gear 88 beinghalf the speed of variator output shaft speed 106.

[0038] The increase in the speed of sun gear 88 increases the speed atwhich planet gears 92, and hence carrier 94, rotate around axis 59. Whenring gear 60 and sun gear 88 are rotating at the same speed, thencarrier 94 will rotate in unison with gears 60 and 88. When the sun gear88 is rotating slower than ring gear 60, carrier 94 will rotate slowerthan ring gear 60, but faster than sun gear 88. When sun gear 88 isrotating faster than ring gear 60, carrier 94 will rotate faster thanring gear 60.

[0039] The relative contribution of the change in speed of the sun gear88 to the change in speed of the carrier 94 depends on the relativediameters of sun gear 88 and ring gear 60 according to the equation:

θ_(C)=(r _(R)θ_(R) +r _(S)θ_(S))/(r _(R) +r _(S))

[0040] where

[0041] θ_(C) is the rotational speed of the carrier 94;

[0042] r_(R) is the radius of ring gear 60;

[0043] θ_(R) is the rotational speed of ring gear 60;

[0044] r_(S) is the radius of sun gear 88; and

[0045] θ_(S) is the rotational speed of sun gear 88.

[0046] In the example of FIG. 2, the ratio of the radius of the ringgear to the radius of the sun gear, (r_(R)/r_(S)) equals 2.5.

[0047] As variator 52 transitions from a maximum underdrive condition toa maximum overdrive condition, variator output shaft speed 106 climbsfrom a low point of approximately 1000 RPM to a high point ofapproximately 6000 RPM, and CVT module output shaft speed 108 fromapproximately 1200 to approximately 1900. When a high point 113 isreached, and variator 52 is in its maximum overdrive condition, a shiftis made within gear unit 20 to a second gear. With the shift to secondgear, variator output shaft speed 106 is dropped back to about 1000 RPMand CVT module output shaft speed 108 to about 1200 RPM. The variatorthen starts its task anew, going from maximum underdrive to maximumoverdrive. This is repeated in third, fourth and fifth gears ifnecessary, until the vehicle is at its desired operating speed.

[0048] The gear ratios of gear unit 20 must be matched with the range ofvariator 52, taking into consideration the ratios of gear sets 62, 82and 54. For the ideal transmission of FIG. 2, gear unit ratios are ofeven steps of approximately 60%, providing coverage compatible with thatprovided by the variator.

[0049] In another exemplary embodiment, an 18 speed geared transmissionwhich would employ 17 shifts or steps of approximately 18% and rangingfrom 17% to 22% to provide a total ratio range from 12.19:1 at the lowend to 0.73:1 at the high end can be replaced with a six speed gear unit20 or transmission coupled with a CVT module 18 providing a 60% range.The six speed transmission with steps of approximately 60%, incombination with a CVT module, provides the same ratio coverage as the18 speed transmission. A transmission having gear ratios would be 10.48,6.55, 4.10, 2.56, 1.60, and 1.0 would, with the CVT module providing a60% range, provide a total ratio range from 13.26 to 79. If the gearingis selected to support a 100% range from the CVT module 18, then a fourspeed gear unit 20 could be employed, with the gears providing steps of100% and the CVT module handling the speed increases between the gears,as well as underdrive below first gear and overdrive beyond fourth gear.Gear ratios would be approximately 8.00, 4.00, 2.00 and 1.00.

[0050] Changing gears must be executed with care so as to minimize anyloss of energy and of speed during shifting. FIG. 2 is idealized andsomewhat unrealistic in that it does not make allowances for thepossibility of vehicle speed drop off during shifting. Alternativemethods of achieving the necessary torque release within the drivetrain10 are available. With one such method, master friction clutch 16 isreleased to permit shifting of gear unit 20 by controller 32 to aneutral condition, much as a vehicle operator would employ a clutchpedal to release torque when shifting. An alternative means of breakingtorque is to manipulate engine fueling by methods well known in the artand analogous to manually executed clutchless or float shifting. Withthe clutchless method, a command from transmission ECU 22 directs engineECU 24 to in turn issue a zero torque command to controller 34, and to,if necessary, provide torque pulses to ensure a torque levelsufficiently low to permit gear disengagement. Once torque is broken,and gear unit 20 is in neutral, synchronization must be achieved tocomplete the shift. Distinct from the prior art which relied on eithermanipulating engine speed or changing the speed of the input shaft 98,the present invention uses variator 52 to adjust the input shaft to asynchronous speed while the engine and input shaft speed are maintainedat the optimal target level 112. Input shaft brake 50 can potentially beemployed to assist the variator 52 in slowing the input shaft and theelements rotating therewith in an upshift.

[0051]FIG. 3 plots illustrate a more accurate portrayal of a drivetrainsystem 10 operating within the limitations of available components. Thedrivetrain system of FIG. 3 is configured to compensate, if necessary,for a drop-off in vehicle speed that can potentially occur during theshift. In that system, a unit having the characteristics of theexemplary Eaton AutoShift transmission discussed above are employed.

[0052] Gear unit 20, if configured consistent with the characteristicsof FIG. 3, has gear ratios of, first through seventh, 9.24, 5.35, 3.22,2.04, 1.37, 1.0 and 0.75. These ratios yield between-gear-steps of 73%,66%, 58%, 49%, 37% and 33%. If even steps were employed, they would allbe 52%. Instead the steps are arranged in a gathered ratios fashion from73% to 33%. As a result, the usable vehicle velocity range for a singlegear ratio of gear unit 20′ changes less from gear to gear than it wouldif uniform gear steps were employed. The gathered ratio steps space outor separate the shift points of the gear unit more uniformly orregularly than would constant steps. As a consequence of the graduatedchanges in steps, less of the variator range would be employed in theupper gears, as evidenced by the decreasing top speed of variator outputshaft speed 106′. Variator output shaft speed in gear seven increasesbeyond that achieved in earlier gears, as there are no additional gearsto shift into. The vehicle's maximum road speed, at the point of maximumvariator overdrive, would be approximately 95 miles per hour (150kilometers per hour). Higher vehicle speeds could only be obtained ifengine speed and input shaft speed 102′ are permitted to increase beyond112′. Also, at higher vehicle speeds, the variator is operated over anarrower range of speeds than at lower vehicle speeds, as is evidentfrom FIG. 3.

[0053]FIG. 3 also differs from FIG. 2 in that input shaft speed is notheld constant after its initial steep climb from zero. The periodbetween points 114 and 112′ indicates that input shaft speed continuesto increase after the initiation of variator adjustment, and has no realequivalent in FIG. 2. While input shaft speed 102′ and variator outputshaft speed 106′ overlap, it is only by coincidence, based on thevariator input gear set ratio, and the planetary gear ratios that thisoccurs. CVT output shaft speed 108′ exhibits a slight discontinuityapproximately coincident with point 114. This may be attributable to theinput shaft speed 102′ dropping just before the initiation of variatoradjustment. The speed multiplication ratio of gear set 62 is 2.5:1, withvariator input shaft speed 104′ being 4000 RPM when input shaft speed102′ is 2500 RPM. The speed multiplication ratio provided by thevariator output gear set 82 is the 0.4:1, the reciprocal of the ratioprovided by the variator input gear set 62. The ratio of the radius ofthe ring gear r_(R) to the radius of the sun gear r_(S) is 1.5:1. Thegear unit ratios are 9.24, 5.35, 3.22, 2.04, 1.37, 1.0 and 0.75.Together, with the CVT module 18, possible ratios ranging from 11.09 to0.50, with an overall 23:1 spread, are provided.

[0054] Another difference is after the shift into the fifth gear ratiowhere input shaft speed 102′ and variator input shaft speed 104′ takeslight dips. This reflects the reduced need for torque at the higherspeeds under steady state driving conditions.

[0055] The drivetrain 10 modeled by FIG. 3 employs a variator having anoverall ratio range of 6:1 and providing an underdrive torquemultiplication ratio of 2.45:1 and an overdrive torque multiplication of1:2.45. It is apparent from the plot of speed 106′ that the full rangeof variator 52 is not being employed. While substantially all of theoverdrive range is being used in first gear to reach point 113′, not allof the range is being used on the underdrive side at the start of secondgear. That provides drivetrain system 10 with a torque reserve availablefor use upon completion of an upshift. No such provision was made in thearrangement of FIG. 2. This advantageously accommodates maintainingconstant engine speed even with the occurrence of a slight drop invehicle speed as might occur when shifting on an uphill grade. The otherupshifts in FIG. 3 maintain a similar reserve. The system has anabundance of low end torque capacity. It is possible to initiate vehiclemovement with the gear unit is second gear, with no need to make theshift to third gear until a vehicle velocity of 13 miles per hour (21kilometers per hour) is reached. Similarly, on the overdrive side, thevariator 52 does not employ the full range available. The ratios used bythe variator after first gear, and in the upper level gears inparticular, are significantly less than the maximum available ratio of1:2.45.

[0056] FIGS. 4-11 provide detailed perspective illustrations of a CVTmodule 18′ mounted to a gear unit 20′. CVT module 18′ is integrated intoa clutch housing 116. A clutch friction disc, not shown, would bedisposed over CVT module input shaft 58′.

[0057] The combined CVT module 18′ and gear unit 20′ of FIG. 4 isoriented so that CVT module 18′ is to the left of gear unit 20′. Theimage of FIG. 4 is upside down relative to the image of FIG. 1, withcontroller 32 being on the bottom in FIG. 4. Typically, controller 32would be toward the top. Transmission ECU 22′ is on the far side of gearunit 20′. CVT module input shaft 58′, a combined CVT module output shaftand gear unit input shaft 96′ and 98′ and a gear unit output shaft 100′are all concentrically located on first axis of rotation 59′. Variatorinput shaft 68′, concentrically located on second axis of rotation 69′,is parallel to and offset from input shaft 58′, and drivingly connectedto input shaft 58′ by gear set 62′.

[0058] As better seen in FIG. 5, input drive gear 64′ of input drivegear set 62′ is fixed to an outer diameter of ring gear 60′. Shaft 58′is rotatably supported within clutch housing 116 by a ball bearing 118.Driven gear 66′ is fixed to shaft 68′. First variator pulley 70′ ismounted to shaft 68′ with part of the actuating mechanism of thedisplaceable flange being shown in section. A variator housing 120combines with clutch housing 116 to enclose variator 52′. Carrier 94retains planet gears 92′. Carrier is fixed to combined shaft 96′ and98′. This configuration beneficially provides a compact arrangement ofthe elements of the CVT module 18′.

[0059]FIG. 6 shows the CVT module 58′ in much the same orientation as inFIG. 5, but outside of the clutch housing 116. FIG. 7 provides asectional view of the CVT module 58′ taken along first axis 59′ andthird axis 87′. Second variator pulley 72′ is shown in section. Outputdrive gear set 82′ includes output drive gear 84′ and output driven gear86′.

[0060] A perspective view of CVT module 18′ is shown from yet anotherangle in FIG. 8. FIG. 9 shows CVT module 18′ in the same orientation asin FIG. 8, with the clutch housing 116 in place. FIG. 10 shows theassembly of FIG. 9 with the variator housing 120 in place. FIG. 11 is anexterior view of the entire CVT module 18′ and gear unit 20′ assembly.

[0061] The present invention is not limited by the preceding descriptionof a specific embodiment of the invention. The scope of the invention isset forth in the claims appended hereto.

I claim:
 1. A continuously variable transmission for use with motorvehicles comprising: an electronic control unit configured to includelogic rules for controlling a transmission, including issuingtransmission control commands; an automated gear unit having gearsproviding a plurality of selectively engaged gear ratios and engagingone of the plurality of gear ratios responsive to commands from theelectronic control unit to do so and the gear unit having a gear unitinput shaft and a gear unit output shaft; a variator having a variatorinput shaft and a variator output shaft and configured to continuouslyvary a ratio of input torque to output torque between the variatorshafts responsive to commands from the electronic control unit, thevariator output shaft drivingly connected to the gear unit input shaft;an input gear set drivingly connected to the variator input shaft; aninput fixed ratio element configured to reduce the torque from the inputgear set to the variator and operably disposed between the input gearset and the variator input shaft; and an output fixed ratio elementconfigured to increase the torque from the variator and operablydisposed between the variator output shaft and the gear unit inputshaft.
 2. A continuously variable transmission as claimed in claim 1wherein the input gear set is a planetary mixer gear set including aring gear and a sun gear and a carrier retaining a plurality of planetgears disposed between the ring gear and the sun gear with at least oneof the ring gear the sun gear and the carrier drivingly connected to thevariator input shaft.
 3. A continuously variable transmission as claimedin claim 1 wherein the gear ratios of the automated gear unit aregathered gear ratios.
 4. A continuously variable transmission for usewith motor vehicles comprising: an electronic control unit configured toinclude logic rules for controlling a transmission, including issuingtransmission control commands; an automated gear unit having gearsproviding a plurality of selectively engaged gear ratios and engagingone of the plurality of gear ratios responsive to commands from theelectronic control unit to do so and the gear unit having a gear unitinput shaft and a gear unit output shaft; a variator having a variatorinput shaft and a variator output shaft and configured to continuouslyvary a ratio of input torque to output torque between the variatorshafts responsive to commands from the electronic control unit; and aplanetary mixer gear set including a ring gear and a sun gear and acarrier retaining a plurality of planet gears with the planet gearsdisposed between the ring gear and the sun gear with the ring gear beingfixed to a mixer input shaft the sun gear drivingly connected to thevariator output shaft and the carrier fixed to a mixer output shaftdrivingly connected to the automated gear unit input shaft.
 5. Acontinuously variable transmission as claimed in claim 4 furthercomprising: an input fixed ratio element configured to reduce the torquefrom the input gear set to the variator and operably disposed betweenthe mixer input shaft and the variator input shaft; and an output fixedratio element configured to increase the torque from the variator andoperably disposed between the variator output shaft and the sun gear. 6.A continuously variable transmission as claimed in claim 5 wherein theinput fixed ratio element is provided by a input drive gear coaxial withand fixed to the mixer input shaft engaging a driven gear coaxial withand fixed to the variator input shaft and the output fixed ratio elementis provided by a drive gear coaxial with and fixed to the variatoroutput shaft engaging a driven gear coaxial with and fixed to the sungear.
 7. A continuously variable transmission as claimed in claim 6wherein the ring gear has the input drive gear affixed to an outerdiameter thereof.
 8. A continuously variable transmission as claimed inclaim 6 wherein the input driven gear and the output drive gear are bothdisposed on a side of the variator proximate to the automated gear unitand the output driven gear is disposed between the planetary carrier andthe automated gear unit.
 9. A continuously variable transmission asclaimed in claim 7 wherein the input driven gear and the output drivegear are both disposed on a side of the variator proximate to theautomated gear unit and the output driven gear is disposed between theplanetary carrier and the automated gear unit.